Painting outside in cold temperatures is very risky business. Many professional exterior painters will not even chance it. Being careful to ensure the paint drys enough before it gets extremely cold is actually much more important than you might think.
On the paint can the directions will tell you can paint at either 35 or 50 degrees and for a specified amount of time. However, the technical data sheets may tell you numbers like “dries to touch in 1 hour” and “Recoat after 4 hours”, some even give different scenarios for this such as 70 degrees or 90 degrees. While all of these times can give you some good guidance in most situations, you are here to find out how to cheat the rules and get the project done properly in adverse situations. SO, here is the simple way to figure just how far you can push the frozen paint envelope.
First Few Minor Standard Rules
- Paint in the sun and be sure the surface will be in the sun long after you finish painting.
- Have ALL prep work completed.
- Have tools organized.
- Keep paint stored in the warmest part of your home until you are ready to use it.
- Read all material data sheets and paint can directions and only consider the information that you collect from these and not what some kid said at the paint counter.
- If the area will be shaded by 3pm then it must be painted by noon.
Why Paint Needs The Higher Temperatures
Non-Oil paint adheres better in the heat to any surface, this is an undeniable truth, although, there are limits to this. Depending on humidity very high temperatures can be devastating as the solvents can be trapped in the paint film causing the paint to completely fail.
Be A Painter – Be A Weatherman Too
Painting in the cold takes some serious determination and know how. Here’s some MUCH better guidance on your weather situation. The paint manufactures would try better to relay this information except for the fact that this would not fit on a paint can or on the tech data sheets. Keep in mind this is only one day in Indianapolis, Indiana.
7am Overnight Low
The overnight low determines how cold your substrate may be in the morning. Start your exterior painting in the sun if you need more heat. Note the humidity at 63% compared to the temp. Also note the wind.
11am Humidity/TempFlip Flop
Actually, this change probably happens more at about 10:30am where the humidity percentage drops below the temperature. This is an important mark as this is when you can actually get good dry times.
4pm Humidity Shift
This is the point where the humidity start to rise again.
8pm Humidity/Temp Flip Flop
This is where the humidity percentage goes above the temperature.
Weather Applicable To Exterior Painting
- Product Temperature – This is the biggest oversight. Nobody considers this factor and this can really help if you are trying to cheat the other factors. Be sure your paint is warm but don’t try to heat the paint! Ever!
- The Low Temp Of Previous Night – The low temperature matters because this is how cold your substrates are.
- If the substrate is under your recommended temperature (either 35 or 50 degrees) then you need to start in the sunniest part of the home.
- If choosing two days where the high and low temperature is similar, choose the day that has the higher previous days’ low.
- Humidity Shifts
- In the morning when the temperature has risen above the humidity percentage this is the best sign that you are in your sweet spot for paint to dry. You can start to apply slightly before this time as long as your air temp and product temp are within guidelines.
- In the late afternoon the humidity will start to rise again usually in accordance with the temperature starting to drop but not always necessarily.
- In the evening after the sun goes down the humidity will rise again above the temperature. At this point paint will not dry anymore.
The Cold Weather Window
The window of acceptable temperatures depends on if you have a 35 or 50 degree paint. However, there is a short window that paint will actually optimally dry. This point is after the “10am humidity/temperature shift” until the “8pm humidity/temperature shift”.
- Painting is not to start before the first Humidity/Temp drop unless the previous low is not below your paints limits.
- All exterior painting should be finished BEFORE the humidity starts to drop for the day. Optimally, in this scenario all painting should be finished by 1pm to allow four full hours of ideal dry time.
- An unusually high low from the previous night will extend the window by allowing you to start much earlier.